Aphis spp.


Aphids may be green, black, brown, red, pink, or some other color depending on the sap color of the host plant. They are usually slow-moving insects with somewhat pear-shaped bodies ranging from 1 /16 to 1 /8 inch long. There may be various sizes of wingless aphids (nymphs and adults) in a dense colony on a stem, on the underside of the foliage, or on the flowers. Later in the season, some may have relatively large, transparent wings. The slender antennae are conspicuous, and near the rear end of the abdomen there are two tubes called cornicles.


Aphids on Pittosporum
Figure 2. Aphids
on Pittosporum

Life History
The life history of aphids is somewhat complicated and varies with the species. One of the less complicated life histories proceeds as follows: Overwintering eggs on branches and stems hatch in the spring to produce a wingless form known as the stem mother. The unfertilized stem mother gives birth to living young in great numbers. Several generations may occur in this fashion, but in due time some individuals will develop wings (alates) and migrate to another host. Here they may deposit eggs for the winter or, after a few generations, migrate back to the original host to lay eggs.


Aphids are sucking insects that feed by thrusting a long beak into the plant tissue. They withdraw great quantities of sap, some of which they execrete as "honeydew". The honeydew makes the plant sticky. When trees are heavily infested with aphids, sidewalks, lawn furniture, and automobiles may become wet with honeydew. A sooty mold often develops with the honeydew blackening stems and foliage. This fungus is not parasitic to the plant, but reduces the amount of photosynthetic area. Leaves of plants may be distorted by aphids feeding on the undersides. Succulent stems may wilt or growth may be arrested by colonies of aphids. On the other hand, damage caused by aphids feeding on the bark of trees or woody shrubs cannot be readily seen.


Green Peach Aphids on Mustard Leaf
Figure 4. Green Peach
Aphids on Mustard Leaf

Nonchemical Control
Plants that are well established and vigorously growing usually can tolerate low to medium aphid population levels. Newly transplanted trees or stressed plants are more vulnerable to aphid damage and control should be considered. Aphid populations are usually controlled later in the season by natural enemies such as parasites, predators, and pathogens. In some cases, populations may crash literally overnite due to weather conditions.

Chemical Control
Apply an insecticide when aphids are numerous. Spray with high pressure and throroughly cover the foliage